How is the adult Central Nervous System neuronal diversity produced from an apparent uniform pool of embryonic progenitors and how the emerging and functional characteristics of different neuronal populations relate to their developmental origin.

Neuronal diversity can be achieved by temporal patterning of neural stem cells. Recent work from the Desplan lab has shown that, like in the ventral nerve cord of Drosophila, a temporal progression of transcription factors in the progenitor cells (neuroblasts) of the developing medulla of the Drosophila optic lobe instructs the orderly production of different neuronal types. Interestingly, in the developing medulla, the transcription factors used in the temporal sequence are different from those in the ventral nerve cord. This suggests that temporal patterning of neuroblasts is a universal strategy used for neuronal specification, with different transcription factor sequences being recruited in different systems. Whether and how the same mechanism is used for other optic lobe and brain neuropils is not known. Here we address this question by investigating neurogenesis in the Inner Proliferation Center (IPC), a region of the Drosophila larval brain that gives rise to the Lobula neuropil, the next processing center that receives inputs from the medulla.

Our initial observations suggest that the neuroblasts from the IPC do not switch expression of their transcription factor and instead are patterned mostly by spatial cues. Therefore, IPC neurogenesis provides a unique opportunity to test how universal the temporal patterning strategy is, and to investigate how other optic lobe neuropils use spatial patterning for neuronal specification.

Furthermore we aim at understanding how the combinatorial code of transcription factors in a developing neuron relates to its emerging and functional characteristics. The deep knowledge of the optic lobe anatomy allows us to make predictions about the role of specific neurons in fly vision. Such predictions will be tested with electrophysiology and with Calcium Imaging in live flies, eventually allowing us to understand how neurons with similar or distinct functions are developmentally related.